1. Field of Invention
The present invention relates to an operation method an electrically erasable and programmable read-only memory device.
2. Description of Related Art
Electrically erasable programmable read only memory (EEPROM) is a type of non-volatile memory that allows multiple data reading, writing and erasing operations. In addition, the stored data are retained even after the power to the device is terminated. A typical electrically erasable programmable read only memory is a flash memory.
According to the different structural materials, a flash memory can be categorized into doped polysilicon floating gate type of memory device and the charge trapping layer type of memory device. In general, the material of the charge trapping layer is silicon nitride, and above and below the silicon nitride charge trapping layer respectively disposed a layer of silicon oxide. Further, the control gate and the substrate are formed with a polysilicon or silicon type of material. Hence, this type of device is normally known as a silicon/silicon oxide/silicon nitride/silicon oxide/silicon (SONOS) device.
According to the various arrangements, a flash memory can also be categorized into NOR type and NAND type. On the other hand, according to the different functions, a flash memory can be categorized into code flash for programming data and data flash for storing data. A code flash memory device is mainly responsible for providing the turn-on and program control of an electronic product; hence, it is mandated for a code flash to be able to read and retrieve data rapidly. On the other hand, it is mandated for a data flash memory device to be able to write data rapidly.
A typical operating method of a NOR flash memory device includes selecting a single memory cell, applying a bias to the word line corresponding to the control gate of the selected single memory cell and a bias to the bit line corresponding to the drain region, applying 0 volt to other word lines, and applying 0 volt to or floating other bit lines. Accordingly, electrons or holes are injected into the doped polysilicon floating gate or the charge trapping layer via the channel hot electron effect or the channel hot hole effect to alter the threshold voltage. However, the programming operation with this type of cell-by-cell writing method is time consuming; hence, the application thereof to a data flash memory device, which requires the function of writing data rapidly, is inappropriate because the throughput is highly limited. Accordingly, a typical data flash memory device is a NAND flash memory device. On the other hand, a NAND flash memory device normally applies the positive Fowler-Nordehim electron tunneling or the negative Fowler-Nordehim electron tunneling, which is inapplicable in a NOR flash memory device. Therefore, a NOR flash memory device is solely applicable on code flash memory device for providing the turn-on and program control of an electronic product.